The George Zimmerman trial has generated conversations across the country about race and perceptions, both conscious and subconscious. And in recent years there's actually been a huge amount of research by social scientists looking into the question of why we view people the way we do and how our subconscious views can differ from what we think we believe.

NPR's science correspondent Shankar Vedantam regularly joins us to talk about the science behind the news. And he's with me now. Good morning, Shankar.

SHANKAR VEDANTAM, BYLINE: Good morning, David.

GREENE: So I think when most people think about racism, we think of it as being motivated by hate or animosity. Now, when scientists actually look at racism, is that what researchers find?

VEDANTAM: I think it's one model of prejudice, David, and it certainly explains the kind of prejudice we might have seen in America in the 1950s or '60s. But there's been a lot of research in the last 10 or 20 years, which really suggests that that might not be the main way prejudice actually takes place today. For one thing, virtually no one today in America admits to being prejudiced. And so you have a paradox: You have racism but not necessarily racist.

GREENE: What is an example of what you just said?

VEDANTAM: So Alexander Green at Massachusetts General Hospital once conducted a study. He had physicians evaluate patients and some of the physicians thought they were evaluating a white patient. And some of them thought they were evaluating a black patient. And what Greene found is that the higher the levels of subtle unconscious stereotypes the physicians held, the more likely they were to not prescribe the black patient with clot-busting drugs for a heart attack.

GREENE: Based on the color of a patient's skin, they were actually treating patients differently for heart problems.

VEDANTAM: Yeah. But here's the important thing, David. The physicians didn't act in ways that were driven by animosity. In fact, when they saw the results, they were horrified. They weren't trying to treat the black patients badly. What was happening really, someone complains of chest pain and you're having to judge: Is this person suffering from indigestion or about to have a heart attack? And in that kind of situation - where you're not completely sure - your biases can help play a very powerful role.

GREENE: OK. If there are biases like this found in doctors who are not showing animosity or hatred, I presume that these types of biases could be widespread. I mean what can we do about them?

VEDANTAM: Yeah, I think they're extremely widespread. And one of the interesting elements of this research is it suggests that these biases are held by the whole culture. Black police officers can be shown to act in biased ways to get black motorist. Or you know, women can be shown to act and sexist ways against other women.

There's been a lot of work trying to figure out how to reverse these subtle stereotypes. And I came by an interesting new study. Calvin Lai and Brian Nosek, at the University of Virginia, they asked teams of scientists to come up with rapid interventions that can reverse these subtle biases. And the scientists came up with 18 different techniques, which they ran on more than 11,000 volunteers to see which of these techniques could reverse these subtle unconscious biases.

GREENE: OK, so what did they find?

VEDANTAM: Well, what they found, David, is that teaching people a history lesson about the injustice of prejudice was completely ineffective. What did work was to expose people to messages that Harvard University psychologist Mahzarin Banaji calls Counter Stereotypical Messages.

MAHZARIN BANAJI: People were shown images or words or phrases that in some way bucked the trend of what we end up seeing in our culture. So if black and bad have been repeatedly associated in our society, in this intervention the opposite association was made.

VEDANTAM: And you know, Banaji told me that she's taken this message to heart herself. She programmed her screensaver to flash Counter Stereotypical Messages at her all day long. And she told me that one image in particular has had an especially strong effect on her.

BANAJI: My favorite example is a picture of a woman who is clearly a construction worker wearing a hard hat, but she is breast-feeding her baby at lunchtime. And that image pulls my expectations in so many different directions that it was my feeling that seeing something like that would also allow me, in other contexts, to perhaps have an open mind about new ideas that might come from people who are not traditionally the ones I hear from.

GREENE: OK. So is that the message here, Shankar: We should fill our days as much as we can with images that break stereotypes and are not what we expect?

VEDANTAM: You know, I think that's certainly what this research suggests is one way to counter these stereotypes. Now, the truth is these interventions are probably not long-lasting. You know, once you leave the office you're not going to see a lot of women nursing their babies at a construction site.

But what I find really interesting about this, David, is that the model of prejudice that this research is pointing to is very different from the model of prejudice that is based on animosity. What it's really suggesting is that our brains are like a car that tends to drift to one side of the road. And Banaji's point is, you may have to lean on the steering wheel a little bit in the opposite direction.

GREENE: It's a metaphor we can relate to. Just keep a little extra pressure on the wheel going in the other direction. Shankar, thanks so much.

VEDANTAM: Thanks, David.

GREENE: Shankar Vedantam, he regularly comes in to talk about social science research. And you can find him on Twitter @Hidden Brain. And while you're at it, follow this program at @nprgreene and @MORNING EDITION.

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